Seismicity of ultraslow spreading mid-ocean ridges at local, regional and teleseismic scales: A case study of contrasting segments

Abstract

The main representatives of ultraslow spreading ridges are the Arctic Ridge System (ARS) and the Southwest Indian Ridge (SWIR). As earthquakes indicate active crustal accretion, monitoring the seismicity provides information about the mechanical state of the lithosphere. The Lena Trough, part of the ARS, spreads obliquely and amagmatic. I relocalized the globally detected earthquakes to show the spatial distribution of the seismicity along the rift axis. During two surveys, our working group recorded the microseismicity of Lena Trough with seismic arrays deployed on ice floes. The second case study concerns the magmatic Orthogonal Supersegment of the SWIR. I accessed the regional dataset of the Neumayer seismic array in Antarctica lying in a distance of ~2100 km to the study area. The dataset contains 743 earthquakes and clearly shows four swarms occurring at an assumed volcanic centre. The new datasets allow a comprehensive evaluation lowering the detection threshold compared to the global station network. Active accretion episodes can be monitored in greater detail showing the spreading mechanisms at contrasting amagmatic and magmatic ridge segments.